I have a couple of vouchers given to me for a change in airfare and a couple of $50 gift certificate vouchers to use on US. Can I make a reservation on line and pay later, do I need to call for reservation then bring the vouchers to the airport, or what? I'm an SP and would rather do it online to track things.

Call and make reservation and within 24 hours take your vouchers to redeem to the airport or ticket office.